Ceramic substrate and process for producing same

Abstract

A ceramic substrate includes a substrate body formed of ceramic and having a pair of surfaces each assuming a rectangular shape as viewed in plane, and a metallization layer formed on the surface of the substrate body and adapted to braze a metal frame thereon. A composite material layer is disposed between the surface of the substrate body and the metallization layer and is formed such that a ceramic portion, a metal portion 10 m formed of a metal similar to a metal component of the metallization layer or a metal which, together with a metal component of the metallization layer, forms an all proportional solid solution, and a glass portion exist together. The thickness of the composite material layer is thinner than that of the metallization layer. A plating layer is deposited on the surface of the metallization layer.

What is claimed is: 
     
       1. A ceramic substrate comprising
 a substrate body formed of ceramic and having a pair of surfaces each assuming a rectangular shape as viewed in plane, and 
 a metallization layer formed on at least one of the surfaces of the substrate body and adapted to mount a metal member thereon, and 
 characterized in that 
 a composite material layer is formed between the surface of the substrate body and the metallization layer and is formed such that a ceramic portion, a metal portion formed of a metal similar to a metal component of the metallization layer or a metal which, together with a metal component of the metallization layer, forms an all proportional solid solution, and a glass portion exist together, 
 a thickness of the composite material layer is thinner than a thickness of the metallization layer, and 
 a plating layer is deposited on a surface of the metallization layer. 
 
     
     
       2. A ceramic substrate according to  claim 1 , wherein the composite material layer is formed on the entirety of the surface of the substrate body. 
     
     
       3. A ceramic substrate according to  claim 1 , wherein a cavity having a rectangular shape as viewed in plane opens at a central portion of the surface of the substrate body, and the metallization layer and the composite material layer are formed on the surface of the substrate body at a portion excluding the cavity. 
     
     
       4. A ceramic substrate according to  claim 1 , wherein a metal frame having a rectangular shape as viewed in plane is joined onto the plating layer via a brazing material. 
     
     
       5. A ceramic substrate according to  claim 2 , wherein the composite material layer contains the metal portion in an amount of 3 vol % to 20 vol % and the ceramic portion and the glass portion as balance. 
     
     
       6. A ceramic substrate according to  claim 3 , wherein the composite material layer contains the metal portion in an amount greater than 20 vol % to 80 vol % and the ceramic portion and the glass portion as balance. 
     
     
       7. A ceramic substrate according to  claim 1 , wherein the composite material layer is a laminate of one or more partial composite material layers which differ in mixing ratio of the ceramic portion, the metal portion, and the glass portion. 
     
     
       8. A ceramic substrate according to  claims 1 , wherein the composite material layer is formed on the surface of the substrate body at at least four corner portions of the surface. 
     
     
       9. A method of manufacturing a ceramic substrate according to  claim 1 , characterized by comprising:
 a step of forming a composite material layer composed of a ceramic portion, a metal portion, and a glass portion on the entirety of at least one surface of a pair of surfaces, each having a rectangular shape as viewed in plane, of a ceramic green sheet, 
 a step of forming a metallization layer on an upper surface of the composite material layer, and 
 a step of depositing a plating layer on a surface of the metallization layer. 
 
     
     
       10. A method of manufacturing a ceramic substrate according to  claim 3 , characterized by comprising:
 a step of forming a composite material layer composed of a ceramic portion, a metal portion, and a glass portion on the entirety of one surface of a pair of surfaces, each having a rectangular shape as viewed in plane, of an upper ceramic green sheet, 
 a step of forming a metallization layer on an upper surface of the composite material layer, 
 a step of punching out, along a thickness direction, a central portion of the upper ceramic green sheet on which the composite material layer and the metallization layer) are formed, thereby forming a through-hole having a rectangular shape as viewed in plane, and 
 a step of laminating a flat lower ceramic green sheet to cover the through-hole on a back surface of the upper ceramic green sheet, and 
 a step of depositing a plating layer on the surface of the metallization layer, the surface having a rectangular shape as viewed in plane as a result of performing the step of forming the through-hole. 
 
     
     
       11. A method of manufacturing a ceramic substrate according to  claim 9 , characterized in that
 as viewed in plane, the ceramic green sheet is composed of a product region where a plurality of substrate regions which are to become ceramic substrates are juxtaposed adjacently in rows and columns, and a edge portion having the form of a rectangular frame and located around the product region, and 
 the metallization layer is formed along four sides of the composite material layer in each of the substrate regions. 
 
     
     
       12. A method of manufacturing a ceramic substrate according to  claim 10 , characterized in that
 as viewed in plane, each of the upper and lower ceramic green sheets is composed of a product region where a plurality of substrate regions which are to become ceramic substrates are juxtaposed adjacently in rows and columns, and a edge portion having the form of a rectangular frame and located around the product region, and 
 the step of forming the through-hole is performed on the upper ceramic green sheet on which the composite material layer and the metallization layer are formed, at a central portion of each of the substrate regions. 
 
     
     
       13. A method of manufacturing a ceramic substrate according to  claim 9 , characterized by having a step of joining a metal frame having the form of a rectangular frame as viewed in plane onto the plating layer via a brazing material after completion of the steps.